Mass spectrometry is a widely used analytical technique for studying molecular structures in organic chemistry and biochemistry. Mass spectrometry techniques involve the production of ionized species from a material sample and the analysis of the species based on their mass and charge. Typically, a spectrum is generated that illustrates the relative abundance of species as a function of their mass (or mass-to-charge (M/Z) ratios in cases when ions may have a charge of greater than 1).
One type of mass spectrometer used for analysis is a time-of-flight mass spectrometer (TOFMS). In a conventional time-of-flight mass spectrometer, the ionized species are accelerated to the same kinetic energy by a potential field, and then allowed to drift in a field free region before striking a detector. The ionized species separate by mass, within the field free region, because lighter ions travel to the detector faster than heavier ions. By detecting the relative amounts of ions at different "flight times", a mass spectrum can be generated.
Tandem mass spectrometers (Tandem MS), including tandem time-of-flight mass spectrometers (Tandem TOFMS) have been developed to provide more information on the material being analyzed and, in particular, to permit improved discrimination between species that have similar mass-to-charge ratios. Typically, tandem MS techniques involve selecting only specific ions, having a particular mass-to-charge ratio, for analysis. The selected parent ions are then dissociated by introducing activation energy to form fragmented ions. The fragmented ions are analyzed to provide the information regarding the structures and origin of the parent molecule.
The following references and U.S. patents describe different mass spectrometry techniques.
Cooks (R. G. Cooks et al., Int. J. Mass Spectrom. Ion Processes. 100, p.209, 1990) discloses mass spectrometry techniques involving surface induced dissociation (SID) of parent ions. SID advantageously enables a high dissociation efficiency for large molecules.
A tandem TOFMS is described by Schey (K. L. Schey et al., Int. J. Mass Spectrom. Ion Processes. 77, p. 49, 1987) which employs a 45.degree. stainless steel target for surface induced dissociation. Another tandem TOFMS is described by Williams (E. R. Williams et al., Int. J. Mass Spectrom. Ion Processes, 123, p. 233, 1993) in which an ion reflector is used as the dissociation target. Though both instruments demonstrated the ability to dissociate relatively large molecules up to mass 1,200 AMU, the instruments had a relatively low mass resolving power for fragment ions.
In U.S. Pat. No. 5,032,722, Boesl describes an MS/MS time-of-flight mass spectrometer. The spectrometer includes an ion source for generating a pulsed primary ion beam, a device for influencing the ions intermittently, in sharply defined areas, and an ion reflector for balancing out time-of-flight differences between ions of identical mass. The reflector includes a movable reflector end plate, which enables primary ions to be eliminated from the spectrum.
In U.S. Pat. No. 5,202,563, Cotter et al., describe a tandem time-of-flight mass spectrometer. The spectrometer incorporates two reflecting-type mass analyzers coupled via a collision chamber. The instrument uses specially designed flight channels that can be electrically floated with respect to the grounded vacuum housing. The design permits either pulsed extraction or constant field extraction of ions from the ionization source, in either low or high energy collisions in the collision chamber.
In U.S. Pat. No. 5,144,127, Williams et al., describes a tandem time-of-flight mass spectrometer that makes use of surface induced dissociation (SID). In one case, the SID surface can be maneuvered within the spectrometer.
Though the above-mentioned U.S. Patents and references describe mass spectrometers having a variety of different configurations, a need exists for a mass spectrometer that can operate in tandem mode to study detailed compositional information of a sample such as specific bond energies.